Field of the Invention
The invention relates to a device for triggering an occupant protection device of a motor vehicle.
U.S. Pat. No. 5,460,404 discloses an occupant protection device in which a series circuit contains an energy source, a first controllable output stage and a parallel circuit containing three series paths each having a firing element and a further controllable output stage. Each firing element is triggered when the common output stage and, at the same time, the firing stages individually assigned to the respective firing element are switched on. In this case, the individually assigned firing stages are controlled by a microprocessor, which identifies an impact on the basis of an evaluation of an acceleration signal. The common output stage is controlled by a customer-specific integrated circuit configuration which monitors the voltage drop across an electromechanical acceleration switch and can thus identify the closing of the switching contacts and hence the necessity of driving the common output stage.
Published, Non-Prosecuted German Patent Application DE 196 25 618 A1 discloses an electromechanical acceleration switch of a testable configuration. The acceleration switch has an acceleration-dependent bending electrode that can be moved in the direction of a fixed electrode. If the fixed electrode and the bending electrode make contact, then the micromechanically configured acceleration switchxe2x80x94between whose fixed and bending electrodes a voltage is present in the contactless state-emits a switching signal in the form of a current pulse, which is identified by a control circuit. Furthermore, such an acceleration switch has a test electrode which, upon application of a voltage, directs the bending electrode toward the fixed electrode on account of electrostatic forces and thus causes, in an electrically controlled manner, the acceleration switch electrodes to close.
If the electromechanical acceleration switch from U.S. Pat. No. 5,460,404 is replaced by a testable micromechanical acceleration switch in accordance with the Published, Non-Prosecuted German Patent Application DE 196 25 618 A1, then it is the case that during the testing of the acceleration switch, the firing of the firing elements is prevented owing to the non-activated output stages that are individually assigned to the firing elements. However, this holds true only insofar as the microprocessor operates without any faults and does not supply a control signal for turning on the output stages. However, if the microprocessor is defective during a test run for the acceleration switch, then there is the risk of occupant-endangering incorrect triggering of one or more restraint devices of the occupant protection system, such as airbags or seat-belt pretensioners.
It is accordingly an object of the invention to provide a device for triggering and a method for operating an occupant protection device of a motor vehicle using a testable acceleration switch which overcome the above-mentioned disadvantages of the prior art methods and devices of the general type, which prevents triggering of a restraint device during an acceleration switch test.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for triggering an occupant protection device of a motor vehicle.
The device contains an energy source, a firing element for the occupant protection device, and an electrically controllable switching device connected to the energy source and to the firing element for transmitting energy from the energy source to the firing element if the switching device is actuated. A control circuit is connected to the switching device for impact-dependent actuation of the switching device, and a testable acceleration switch generates a switching signal. The occupant protection device is triggered if the switching device is actuated and the testable acceleration switch supplies the switching signal to the switching device. A blocking device is connected between the switching device and the control unit, the blocking device prevents the actuation of the switching device during a test of the testable acceleration switch.
The invention provides a blocking device which prevents the actuation of the switching device during a test of the acceleration switch and whose hardware is preferably configured independently of the control circuit. For the duration of the acceleration switch test, that is to say at least for the duration in which the contacts of the acceleration switch are closed, the blocking device prevents triggering of the firing element, even if the switching device is driven on account of a trigger signal from the microprocessor.
By way of example, if the control circuit is configured as a microprocessor, then the blocking device is preferably not configured as a software function of the microprocessor but as an autonomous component, for example on a carrier configured separately from the microprocessor. This further reduces the probability of incorrect triggering.
In accordance with an added feature of the invention, a monitoring device is connected to the control circuit. The monitoring device generates an enable signal received by the switching device in dependence on an operating state of the control circuit that has been determined, and the switching device can be actuated by the control circuit only if the enable signal is present.
In accordance with an additional feature of the invention, the control circuit outputs an operating control signal; and the monitoring device is configured for checking the operating clock signal output by the control circuit, and the enable signal is output by the monitoring device as long as the operating clock signal has no irregularity.
In accordance with another feature of the invention, the blocking device receives the enable signal from the monitoring device and can interrupt the enable signal so that it is not received by the switching device.
In accordance with a further feature of the invention, the control circuit generates a test signal received by the testable acceleration switch and the blocking device, the blocking device being activated with the beginning of the test signal.
In accordance with another added feature of the invention, a timing element is connected to the testable acceleration switch, and the timing element supplies the switching signal, which has a defined time duration, if the testable acceleration switch is activated.
In accordance with another additional feature of the invention, the blocking device is deactivated at the end of the switching signal.
In accordance with another further feature of the invention, the blocking device is formed of hardware that is independent of hardware forming the control circuit.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a method for operating an occupant protection device of a motor vehicle. The method includes the steps of:
triggering the occupant protection device if a testable acceleration switch supplies a switching signal and an electrically controllable switching device is actuated by a control circuit in an impact-dependent manner;
actuating and testing the testable acceleration switch; and
preventing the switching device from being actuated during the testing of the testable acceleration switch.
In accordance with an added feature of the invention, there are the steps of determining an operating state of the control circuit; and enabling the switching device in a manner dependent on the operating state that has been determined. The switching device only being able to be actuated if the switching device is enabled for actuation.
In accordance with another feature of the invention, there is the step of monitoring an operating clock signal of the control circuit and enabling the switching device as long as the operating clock signal has no irregularity.
In accordance with an additional feature of the invention, there is the step of interrupting the enabling of the switching device during the testing of the testable acceleration.
In accordance with a further feature of the invention, there is the step of generating a test signal for closing acceleration switch contacts of the testable accelerating switch and interrupting the enabling of the switching device at a beginning of the test signal.
In accordance with a concomitant feature of the invention, there is the step of providing the switching signal of the testable acceleration switch with a defined time duration and the interruption of the enabling of the switching device is cancelled with an end of the switching signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for triggering and a method for operating an occupant protection device of a motor vehicle using a testable acceleration switch, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.